


sine pi equals love

by crocustongues



Category: Haikyuu!!
Genre: M/M, Mutual Pining, Tutor AU, shirabu kenjirou is a dense loaf of sourdough, yahaba shigeru is a good friend
Language: English
Status: Completed
Published: 2018-02-09
Updated: 2018-02-09
Packaged: 2019-03-15 20:10:22
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,892
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13620810
Author URL: https://archiveofourown.org/users/crocustongues/pseuds/crocustongues
Summary: In which Shirabu tutors Futakuchi at maths, and gets swept up in him and finds that sometimes, it's good to let go of things and introspect.





	sine pi equals love

**Author's Note:**

  * For [Beewachan](https://archiveofourown.org/users/Beewachan/gifts).



> sine of pi is zero idk what this means for their relationship but thats exactly the number of fucks i give abt maths.
> 
> sorry it took 10 years beewa chan i luv u whole lot n i hope u do well at calculus hbkshvb

Sometimes, Shirabu hates how extroverted his mother is. She can (and will) strike up a conversation about the most mundane things with the postman, their neighbours, or the cashier at the _konbini_ around the corner. He’d observed others’ mannerisms, over the years—how some people crack their knuckles, some squish their eyebrows together, Yahaba bites his fingernails, and Shirabu’s mother _makes friends_.

Over the years, the fact has posed several problems to him. He’s managed to weasel himself out of quite a few, but some just have to be faced with courage and perseverance. And patience. Lots and _lots_ of patience.

“You’re going to like it, believe me! It’s quite an enriching experience!” Shirabu’s mother tells him, her sunny disposition making it rather hard for him to disagree.

“I’m sure,” he says instead, hoping she’ll just forget about this entire ordeal. Except, his mother, like all mothers and elephants and Yahaba when money is involved, never ever forgets anything.  
“Kaede-san tells me her son really needs to pass his course if wants to maintain his spot on the volleyball team. I’d thought you of all people would be a little more empathetic about this.” Shirabu knows not to look over right about now. His mother is using her Neutral Tone of You’ll Do What I Want Because You Know I’m Right.

“Yes, Mother,” Shirabu sighs. She knows him well enough to say the magic three-syllable word - _volleyball_. Maybe, if this guy didn’t turn out to be too annoying, they could even play a couple of games.

“Great! Here’s Kenji-kun’s number, and make sure you call him tonight. I want to hear about a schedule, alright? Who knows, maybe it’ll do you some good to have friends for a change.”

“I have friends!”

“Shigeru-kun doesn’t count because you’re in different countries now! It’d be good for you to have some real people contact, Kenjirou.”

“Don’t make it weird, we’re probably not even going to have anything in common.” And Shirabu hopes he’s wrong on all accounts because he, unlike what a certain Yahaba Shigeru thinks, isn’t a giant masochist. He does want to gain something from this experience, and this _Kenji-kun_ sounds like a lesson in diplomacy and teaching skills. And patience, of course. Something he’s aware he lacks on all fronts.

 _Sigh_. His mother’s too nice for her (and her son’s) own good.

✼　 ҉ 　✼　 ҉ 　✼

Shirabu’s hand hovers over the send button, suddenly unsure, when suddenly a message pops up.

 **[unknown number]** :hey tutor-san it’s me kenji just wanted to check if tmorrows cool w u

 _Here we go_ , Shirabu rolls his eyes at ‘tutor-san’, and texts back in affirmative, immediately switching chats to text Yahaba, who has thus far, sent twenty two laughing emojis and two crying ones.

 **Me** : He wants to meet up tomorrow.

 **Shigeru** : k use condoms

**Me** : I hope you choke on air. 

**Shigeru** : dude ly2 

**Shigeru** : deetz 2moro, facetime me 

**Me** : OK. 

Shirabu sighs and hopes for the best. 

✼　 ҉ 　✼　 ҉ 　✼

Shirabu soon finds that Kenji-kun is a tall lanky mass of _dumbass_ who introduces himself as Futakuchi Kenji.

“No, it’s _sine_ of pi! We just went over that!” Shirabu grits his teeth and swallows his anger. It wouldn’t do to kill his student on the first day of class, would it? 

Futakuchi makes an unholy sound of frustration and Shirabu’s mind is equal parts in agreement and in absolute rage. They’d been over this particular kind of sum _four_ times already and it was starting to grate on Shirabu’s nerves, and it is on this note their first session ends fifteen minutes and not a single finished sum later.

Still, it appears that Futakuchi is trying and Shirabu can’t find fault with that. What he can’t get behind is that he’s starting to suspect Futakuchi’s perfectly capable of doing the sums himself and is just here to _waste_ Shirabu’s time. Some days he’d arrive at Shirabu’s, sweaty and unbearable, complete with a smug look and a smug attitude and in the middle of, say, geometry, he’d suddenly launch into a story about the dogs he’s seen around in the campus and Shirabu would find himself swept into conversation and, dare he say it, _invested_ even, in the story. Needless to say, it infuriates Shirabu to no end.

He says as much to Yahaba over the phone one evening, belatedly realising that Yahaba wasn’t even _good_ at giving advice. But Yahaba makes up for it by scoffing and _tch_ —ing at the right moments. 

“—and he didn’t even, can you imagine! Mother asked him if he wanted to stay for dinner and he said _yes_. The look in his eye, I shit you not, Shigeru, was pure, 100% undiluted malice.”

Maybe Shirabu has been exaggerating a little. When Shirabu’s mother, bless her friendly, loving heart, had invited Futakuchi to stay over for dinner, Futakuchi’s eyes had, admittedly, lit up. Shirabu had noticed that Futakuchi had, admittedly, been looking a little worse for the wear, but he’d still, admittedly, tried to signal to his mother to abort the mission.

[“Kenji-kun seems like a nice, charming boy, don’t you think?” Shirabu’s mother says, once they wave Futakuchi goodbye.

Shirabu adamantly thinks the opposite—Futakuchi was charming, but in all the wrong ways. He huffs a little and his mother laughs.

“A little dense, perhaps a tad tactless, but charming nonetheless. What do you think, Kenjirou?”

Shirabu makes a noncommittal grunt and walks to the kitchen to wash the dishes.]

“I don’t get it,” Yahaba interjects as soon as Shirabu takes a second to breathe, “why are you so hell bent on demonising this guy?” he pauses, before continuing, “Heh, no pun intended.”

“Haven’t you been listening? He’s an asshole, he’s even got my mother on his side!”

“Says you, who has made up his mind to not allow him a single chance to prove himself. Maybe try not being a complete hardass for once in your life.” Damn it, Yahaba was _terrible_ at advice.

“Yeah, yeah, whatever,” Shirabu mumbles, trying not to feel like he’d just been caught red-handed.

“You know I’m right. Say hi to everyone! Bye!”

✼　 ҉ 　✼　 ҉ 　✼

Shirabu’s minding his business one evening, glaring at the graphs in his economics textbook, when his mother calls for him from downstairs. He sighs and thinks it’s probably for the best because between tutoring Futakuchi and drawing (and redrawing) wonky graphs without a ruler, he’s going to go mad if he doesn’t take breaks now and again.

His mother looks excited and her enthusiasm was infectious. Shirabu knows to approach it with a tinge of caution.

“Kenjirou! Kaede-san’s asked us to come over this weekend for dinner! Isn’t that fun?” She goes on for a bit about Kaede-san, but Shirabu’s stuck on the thought that if he’s right (he really, _really_ hopes he isn’t), Kaede-san is Futakuchi’s mother. And that would mean this weekend, three days away, he’d have to go to Futakuchi’s house. 

“—Tell Kenji-kun to say thanks. Kenjirou? _Kenjirou_? Are you listening?”

“Wha—Yes, of course. I’ll tell him.” Shirabu’s heart feels like it is in literal pieces.

✼　 ҉ 　✼　 ҉ 　✼

“ _Oh my gosh_ , can you not make a big deal about _everything_?” Yahaba sounds exactly as Shirabu had imagined he would—annoyed and about to say something that’s going to make Shirabu regret their friendship.

“But this _is_ a big deal!”

“You’re obsessing over him. Have you considered, oh my god,” Yahaba inhales loudly and obnoxiously, as he is wont to do when he’s about to say something Shirabu would definitely 100% deck him for, “have you ever stopped to think that maybe, just maybe, you’re so stuck on this guy because you _like_ him?”

And just like that Yahaba’s line goes dead.

“You’re being a coward, you know!” He shouts, even though no one can hear him, except his sister, who yells at him to shut up from her bedroom next door.

✼　 ҉ 　✼　 ҉ 　✼

Saturday evening rolls around quicker than Shirabu’s heartbeat these days, and both he and Futakuchi have done a splendid job of ignoring the elephant in the room.

(Instead, Futakuchi talks trash about his volleyball team and Shirabu listens, in spite of himself.)

“Kaede–san! Thank you for having us over!” Shirabu’s mother says as they’re ushered in by the infamous Kaede-san herself. She looks remarkably like her son, and there’s a tiny version of herself, maybe eleven or twelve years old at best, hiding behind her.

“This is my daughter, Sayaka,” and mini-Kaede-san waves at them.

Sayaka, who has the same look of I’m Done as Futakuchi when he’s faced with a set of trigonometry word problems, allows Shirabu’s mother to coo over her for a few minutes before the man himself, Futakuchi Kenji, decides to make an entrance.

“There you are Kenji, I was starting to wonder if you’d been washed away in the shower. Come say hello, and lay the table for dinner.”

It turns out—Futakuchi was a whole ‘nother basket of good, organic, free-range eggs in front people who aren’t Shirabu Kenjirou. Shirabu does the only thing he deems appropriate in that moment—he waves awkwardly. To his enormous surprise, Futakuchi waves back and looks away. _Rude_ , Shirabu thinks before following everyone into the living room.

“Kenji says you’re a really good teacher, is that true?” Sayaka asks, eyes open wide.

“Yeah, I guess,” Shirabu replies, a little suspicious.

“Could you help me with my maths homework, too? Pretty please?” Somehow, Sayaka’s eyes get wider and Shirabu sighs and wonders what it is about him that makes the Futakuchi family want him to do their maths homework for them.

“Saya-chan, don’t annoy him, now. Kenjirou-kun, you don’t have to—“

“It’s no problem, Futakuchi-san, I’d like to help out as much as I can.” He can physically feel his soul leave his body as he follows Sayaka and sits down at the desk to do some good old seventh grade maths while Kaede-san is no doubt whispering words of praise to his mother one room over.

By the time dinner rolls around half an hour later, Shirabu’s extremely thankful that being absolutely shit at maths is a Futakuchi Kenji exclusive affair.

“Thank you Shirabu-san,” Sayaka says, as she shuts her books when her brother comes in to drag them to go eat dinner.

“No problem,” he tells her.

“Hey, how come you’re never that nice to me when I come over?” Futakuchi asks, affronted.

“That’s because you’re a dick.”

“Hey, some of us are not teens yet and can’t swear,” Futakuchi hisses, dramatically pausing to cover his sister’s ears.

“Watch your fucking hands, Kenji,” Sayaka says, before grabbing Shirabu by the wrist and saying, “we should wash our hands first! Come with me.” And Shirabu’s too stunned to say anything as they leave a fuming Futakuchi behind, grumbling about his goblin sister.

“I’m not the goblin, he is,” Sayaka whispers and Shirabu laughs in surprise. Sayaka looks absolutely delighted.

Dinner is a quiet affair, the food is delicious and Shirabu’s finding himself more and more at home as he chews his fish in a surprisingly amiable mood. His mother and Kaede-san are talking about their friends, and Sayaka and Futakuchi seem to be having an argument entirely through facial expressions. Shirabu’s been around the Yahaba household often enough to know this was a common occurrence with siblings but he’s wholly amused at exactly how funny this was to an outsider like him. He doesn’t say it aloud, though, and tucks it into the corner of his mind he’s started to call the Futakuchi Centre of Irrelevance.

The rest of the dinner passes without a hitch—Kaede-san and her husband ask him how he’s doing at school, Sayaka seems to have taken a liking to him, and surprisingly, Futakuchi’s company is tolerable. Enjoyable, even, if Shirabu’s feeling charitable.

His mother’s finally saying goodbye to Kaede-san and Sayaka’s chattering to him while he’s tying his shoelaces when he notices Futakuchi lingering behind his mother, staring right at them with an indiscernible expression on his face. He excuses himself (and later, he’ll blame it on his good mood and the good food), he makes his way to Futakuchi and thanks him. Futakuchi, who now looks surprised and embarrassed and murmurs a thank you back.

‘Why are you thanking me?” Shirabu asks, confused.

“For coming, I guess.”

Before he can reply, his mother calls for him, so all Shirabu does can say is a quick goodbye.

“See you tomorrow!” Futakuchi calls from the doorway and Shirabu turns and waves.

They walk for a bit in silence, the evening is chilly and beautiful, and they still feel too full to do much else. 

“So, I gather you and Kenji-kun get along fine, now?” Shirabu’s mother says, smiling fondly at her son.

“I guess,” Shirabu replies after a beat of silence, because he doesn’t _hate_ hate Futakuchi. Not really. 

“You like him, then,” the Yahaba voice in his head taunts. 

“Do you like him, then?” His mother asks.

Shirabu wonders, sometimes, if Yahaba and his mother were the same person.

“No!” he shakes his head vehemently, like it’d literally knock the thought out of his brain. 

His mother only laughs, like she knew something he didn’t.

✼　 ҉ 　✼　 ҉ 　✼

Futakuchi turns up the next day with a singular rose saying it’s from his sister for helping her with maths.

“She hopes you’ll come visit soon,” he says, ears turning red.

“That’s…that’s really sweet, tell her I said thank you.” Shirabu supposes he’s never really been well liked, not by his peers or his friends. He wasn’t used to receiving nice compliments or sweet  
gestures, other than the hair ruffles he got from his mother (who, by virtue of her title, was duty bound to do Embarrassing Mom Things) and from Yahaba (who doesn’t live here anymore, much to Shirabu’s chagrin, but, like, in secret). So he’s understandably a little mystified by the Futakuchi family and their liking towards him.

He finds that he really likes it, though.

✼　 ҉ 　✼　 ҉ 　✼

“—so obviously, you know, they got together, and everything’s fine now, but I’ve spent a good majority of my day yesterday trying to sort out misconceptions. It’s like Romeo and Juliet, or whatever, I guess,” Futakuchi says, twirling his pencil around.

“Is that why you still haven’t started your probability assignment?” Shirabu says, clearly amused but trying (and failing) at keeping it in check.

“Aww, Shirabu, back me up here. Have you never felt the throes of passion between two individuals who’re clearly, _clear as day_ , mind you, in love with each other, wouldn’t you do everything to get them together?”

“Oh, and you’re the great and benevolent Futakuchi Kenji, here to play cupid?” Shirabu teases.

“More like wishing they quit whining about it to me every day. If you like someone, you like ‘em and then you tell them, and not whine about it to people who don’t care.”

“Wow. That’s harsh.”

“Really? It’s fair, though. I’m allowed to complain about people complaining to me.”

“No I mean—if you think it’s easy for people to just…confess their feelings to someone, you’re wrong.”

Futakuchi stops fidgeting with the pencil, letting it drop and marking his notebook, and looks wide-eyed at Shirabu.

“Shirabu.”

“Futakuchi.” The light-hearted atmosphere evaporates and all that’s left of it is a bitter taste at the back of Shirabu’s throat.

“Do you like someone?” Futakuchi asks, scooting over to sit right next to Shirabu.

Shirabu’s faced several hardships in his life, if you ask him. Crushing on someone, however, was _new_. Harder, still, was the crushing realisation that the person he liked was sitting right next to him, clearly awaiting an answer. 

“You like him!” The Yahaba voice says smugly in his head—the voice he’s now accepted is his conscience and does a _terrible_ job at counselling him and is even worse than Futakuchi himself when it comes to timing.

He’s come to the final conclusion that he does, in fact, have a ginormous crush on the dumbass sitting next to him, and he’s ready to burst with this sudden understanding of his own mind. Does he want this? _No_. Does his brain (Yahaba voice and all) care? _Also no_.

“No, don’t think so, never have, never will. It’s a waste of time don’t you think?” He says instead, too quickly for his liking. To his surprise, Futakuchi’s face falls.

“Oh. That’s not really surprising,” he says, shrugging, as if Shirabu’s heart didn’t really, actually, literally, break into two (million) pieces in the last five seconds.

“Yeah. Hey, I’m not feeling too great right now, could we continue the tutoring later? I, uh. Don’t. Feel well.” Shirabu’s not incredibly gifted when it comes to lying glibly but he tries his best to sound convincing.

Futakuchi looks over curiously, shrugs again, and begins to put away his things.

“I’ll, uh. I’ll call you. Later. To let you know when I’m feeling better?”

“Alright, whatever you say,” Futakuchi stands up and leaves without a backward glance.

And just like that, Shirabu finds that in addition to making friends, keeping them is also something they don’t teach at school. Especially a friend you _like_. Like, _like_ like.

It _sucks_ and Shirabu throws himself on the bed, wishing the day would end already.

✼　 ҉ 　✼　 ҉ 　✼

“Kenjirou? _Kenjirou_? Are you OK? You’ve been lying in bed all evening, are you feeling alright?”

Bless his mother, but also darn her, because Shirabu cannot, under any circumstances, lie to her.

“Not really,” he calls back, rolling over to find a cooler spot on his pillow.

“Sweetheart, do you want some tea? Stay in bed, I’ll bring it up soon.”

 _Bless his mother_ , Shirabu thinks, before drifting off to sleep.

✼　 ҉ 　✼　 ҉ 　✼

It’s been three whole days since the Day.

Somehow, since the Universe and Shirabu are Not Friends, he’s managed to actually fall sick. Today he’s dragged himself to his first lecture, where, since he’s been sick the last couple of days, he hadn’t known there was a quiz. He manages to mark four Bs in a row and then stops caring.

Next, because Someone Out There is out for his blood, he’s somehow managed to simultaneously develop a massive, throbbing headache, and forget his assignment on cost accounting at home. His professor, however, doesn’t care, and yells at him until his ears feel like they’re going to drop off. 

The last straw is during the ten minute break between his Microeconomics class and his Advanced Maths lecture, when someone bumps into him, making him drop his notebooks.

Naturally, he drops his standards and begins to cry, too.

Needless to say, it hasn’t been a good day. It hasn’t even been an OK day. He’s been thinking on and off about Maths and Futakuchi and Futakuchi doing maths. He feels incredibly guilty for shooing him away and blatantly ignoring him until he passes out on his bed at 3:34 pm.

There’s a crash somewhere to his left that wakes him and he looks around blearily, trying to move his fringe out of his way without actually moving his arms. All he can see is Futakuchi holding a bowl of soup. He groans and turns over, trying to fall back asleep, hoping it’s going to change the direction this dream is taking.

“Shirabu, no—here, turn around, I’ve brought some soup! You need the energy.”

Shirabu, in the haze that is his existence, complies.

“There we go. Here, open your mouth. It’s not too hot.” 

Shirabu’s suddenly glad the dream hasn’t changed.

“Why are you here?” he asks, wishing his voice didn’t sound like someone had rubbed sandpaper down the length of his throat.

“Mami-san said you were sick, so mom made you some soup and insisted I take it to you. Your mom sent me up here with strict instructions to make you finish the entire thing. No excuses.”

“Oh.” Shirabu slurps the soup in silence. Given that he can’t taste much, he still thinks it’s fantastic and tries to make a comment but Futakuchi beats him to it.

“Hey, Shirabu. I, uh. Have something to say.” Futakuchi looks the way he did at the dinner at his house. Only now, to Shirabu’s feverish mind, the indiscernible expression showcases the nervousness he’s trying to cover up.

“I know you found it a little, I don’t know, strange? That day? When I asked if you had a crush on anyone? God, maybe I shouldn’t be talking about this when you’re sick, but I—“ he stops suddenly, as if trying to gather his words before they all come tumbling out of his mouth. Shirabu motions for him to continue, sipping on his soup.

“I, uh. You spaced out. For a while. And I was going to say that I,” he swallows hard (and Shirabu’s body feels like it’s been turned to stone), “I really like you. I think you’re really smart and you’re funny when you want to be, only it’s not outright I’m-making-a-joke funny, it’s more witty and sarcastic. Which is great, because when I make a snarky comment, you laugh and you’re really grumpy, like, 90% of the time but it’s worth it I guess—“

At this point Shirabu’s stopped listening because his crush, his stupid, dumb as shit, thickheaded crush, had admitted to liking him, Shirabu Kenjirou, the real life Grinch (except less seasonal).

“I—“ he begins and backtracks, not knowing how exactly to articulate his thoughts and instead takes another sip of his soup.

“No it’s fine, I just had to get it out, I’ll, uh, be going now. Get better soon.” He smiles a wobbly smile at Shirabu and gets up and Shirabu, in his haste to stop Futakuchi, grabs his arm and opens his mouth.

Only, instead of ‘I like you too, please don’t leave’, soup falls out of Shirabu’s mouth.

They stare at each other, with soup in Shirabu’s lap for a solid ten seconds before Futakuchi lets out the loudest guffaw Shirabu’s ever heard in his entire life.

“Shut up, I couldn’t let you go without saying I like you too,” Shirabu says, only, his head is buried in his hands and it comes out garbled and Futakuchi just laughs harder.

“Can I assume you like me back?” He asks, finally calming down, smiling, genuinely smiling, with not an ounce of malice (real or imagined) on his face, directed entirely at Shirabu, whose heart is, naturally, racing faster than a Mach 1 car on the tracks.

“I hate you.”

“Aw, really?”

A beat of silence and Shirabu sighs in defeat.

“Not really.”

And Futakuchi’s smile widens.

✼　 ҉ 　✼　 ҉ 　✼

“OK, so, I repeat for the fifty billionth time. It’s _sine_ pi.”

Futakuchi sighs and return to his problem set and gets to work, tongue sticking out in concentration. It feels a little like déjà vu to Shirabu, except this time, there’re three things that are different.

One: there’s two hands on the table, fingers interlaced.

Two: a half-empty pack of sour gummies bought earlier that day from the konbini around the corner that Shirabu thought Futakuchi would like.

(He was wrong. Futakuchi _loved_ them).

And three: after Futakuchi’s done with his problem set (correctly with no mistakes at all), Shirabu will kiss him softly on the lips and Futakuchi will smile impossibly wide and for a while, maths will be forgotten.

**Author's Note:**

> uh yeah hope u liked that trainwreck of emotions it was fun to write hahaha i's not really slow burn but it's slower than anything ive written before this so let me know if u liked it!!!! i would like to be validated thank u
> 
> (like. for real pls,)
> 
> my tumblr: @iceandbrimstone


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